Cancer is a leading cause of death in the United States and elsewhere. Depending on the type of cancer, it is typically treated with surgery, chemotherapy, and/or radiation. These treatments often fail, and it is clear that new therapies are necessary, to be used alone or in combination with classical techniques.
One approach has been the use of adenoviruses, either alone or as vectors able to deliver anti-cancer therapeutic proteins to tumor cells. Adenoviruses are non-enveloped icosohedral double-stranded DNA viruses with a linear genome of approximately 36 kilobase pairs. Each end of the viral genome has a short sequence known as the inverted terminal repeat (or ITR), which is required for viral replication. All human adenovirus genomes examined to date have the same general organization; that is, the genes encoding specific functions are located at the same position on the viral genome. The viral genome contains five early transcription units (E1A, E1B, E2, E3, and E4), two delayed early units (IX and Iva2), and one late unit (major late) that is processed to generate five families of late mRNAs (L1-L5). Proteins encoded by the early genes are involved in replication, whereas the late genes encode viral structural proteins. Portions of the viral genome can be readily substituted with DNA of foreign origin and recombinant adenoviruses are structurally stable, properties that make these viruses potentially useful for gene therapy (see Jolly, D. (1994) Cancer Gene Therapy 1:51-64).
Currently, the research efforts to produce clinically useful adenoviral therapy have focused on the adenoviral serotype, Ad5. The genetics of this human adenovirus are well-characterized and systems are well described for its molecular manipulation. High capacity production methods have been developed to support clinical applications, and some clinical experience with the agent is available. See, Jolly, D. (1994) Cancer Gene Therapy, 1:51-64. Research related to the use of human adenoviruses (Ad) in cancer treatment has focused on the development of Ad5-based adenoviruses that have a higher potency in, or are preferentially targeted to, specific tumor cell types and there exists a need for generation of more potent oncolytic viruses if adenoviral therapy is to find practical application in a clinical setting.
Ad5 is only one of 51 currently known adenoviral serotypes, which are classified into subgroups A-F, based on various attributes including their hemagglutination properties ((see, Shenk, “Adenoviridae: The Viruses and Their Replication,” in Fields Virology, Vol. 2, Fourth Edition, Knipe, ea., Lippincott, Williams & Wilkins, pp. 2265-2267 (2001)). These serotypes differ at a variety of levels, e.g. pathology in humans and rodents, cell receptors used for attachment, but these differences have been largely ignored as potential means to develop more potent oncolytic adenoviruses (with the exception of fiber alterations, see Stevenson et al. (1997) J. Virol. 71:4782-4790; Krasnykh et al. (1996) J. Virol. 70:6839-6846; Wickham et al. (1997) J. Virol. 71:8221-8229; Legrand et al. (2002) Curr. Gene Ther. 2:323-329; Barnett et al. (2002) Biochim. Biophys. Acta 1-3:1-14; U.S. patent application Ser. No. 2003/0017138).
Exploitation of differences among adenoviral serotypes may provide a source of more effective adenoviral-based therapeutics, using novel adenoviruses with increased selectivity and potency. There is a need for such improved adenoviral-based therapies.